This invention relates to a data exchange for exchanging an input data block into an output data block to carry out transmission of the output cell data block.
It is to be noted throughout the instant specification that a data exchange is for use in an asynchronous transfer mode (ATM) communication system and may therefore be called a cell data exchange for exchanging an input data block into an output data, although this invention may not be restricted to the cell data exchange. The cell data exchange comprises first and second exchanging sections each of which exchanges an input cell data block into an output cell data block. One of the first and the second exchanging sections serves as an active exchanging section. Another one of the first and the second exchanging sections serves as a stand-by exchanging section. It is well known in the art that the first and the second exchanging sections have first and second buffers, respectively. When the first exchanging section is operated as the active exchanging section, the first buffer memorizes a plurality of input cell data blocks as memorized cell data blocks. Each of the memorized cell data blocks is read as the output cell data block out of the first buffer. On the other hand, the second buffer is empty during operation of the first buffer.
A conventional cell data exchange further comprises a receiving section and a transmitting section. The receiving section is operable to receive a received cell data block and to supply the received cell data block as the input cell data block to the active exchanging section, for example, the first exchanging section. The transmitting section is for carrying out transmission of the output cell data block.
It is assumed that the first exchanging section serves as the active exchanging section and the second exchanging section serves as the stand-by exchanging section, as mentioned above. Under the circumstances, let the first exchanging section be often changed to the stand-by exchanging section according to a result of a situation of the first exchanging section under control of a control unit in the following manner. In this event, the receiving section at first stops receiving the received cell data block. In addition, the first exchanging section stops producing the output cell data block. As a result., some memorized cell data blocks are held as residual cell data blocks in the first buffer. The residual cell data blocks are transferred to the second buffer through a transfer path. Therefore, the second buffer has the same contents as the first buffer. After transfer of the memorized cell data blocks is finished from the first buffer to the second buffer, the first exchanging section is finally changed to the stand-by exchanging section and the second exchanging section is concurrently changed to the active exchanging section.
However, it is difficult to quickly change the first exchanging section to the stand-by exchanging section in the conventional cell data exchange because it is necessary to transfer the residual cell data blocks held in the first buffer to the second buffer. In addition, the conventional cell data exchange is disadvantageous in that congestion occurs among the received cell data blocks on a reception path connected to the receiving section because the receiving section stops reception of the received cell data blocks. As a result, some received cell data blocks are lost on the reception path so that loss occurs to the input cell data blocks during transfer of the residual data block from the first exchanging section to the second exchanging section.